Well pipe such as coiled or threaded production tubing, for example, is surrounded by an annular space between the exterior wall of the tubing and the interior wall of the well casing or borehole wall. Frequently, it is necessary to seal this annular space between upper and lower portions of the well depth. Appliances for accomplishing the sealing function are known in the well drilling arts as “packers”. Traditionally, the sealing element of a packer is a ring of rubber or other elastomer that is in some manner secured and sealed to the interior well surface which may be the interior casing wall or the raw borehole wall. By compression, for example, the ring of rubber is expanded radially against the casing or borehole wall.
“Bridge plugs” are well appliances for obstructing the flow continuity of an entire bore; whether it is the entire cross-section of the wellbore, the cross-section of a well casing or the cross-section of a production tube.
One of the greater utilities for a well packer or bridge plug is to isolate a designated section of well bore along the wellbore length that penetrates a particular zone or earth strata. In some cases, the isolated zone may be burdened with an inordinately high internal pressure. For that reason, the packer or bridge plug may be called upon to confine an unusually high pressure differential.
In other cases, where the packer engages the raw borehole wall to seal the annulus, for example, the packer must tightly and continuously engage a rough and highly irregular wall surface.
Either of the two examples above necessitate unusually high applications of setting force against the sealant to attain the degree of rigidity and seal quality required with elastomers having the essential stiffness and other properties necessary to confine high differential pressure loads or expand into deep contours. However, high force and stress loads on a well tube also introduce the potential for other forms of tool and equipment failure.
Reactive Element Packers or REPackers available from Baker Oil Tools are commercial isolation tools that use elastomer swelling technology to provide a barrier in casing/open hole and casing/casing annuli. Such packers may have a water reactive section, an oil reactive section, or both. A water reactive section may consist of water-absorbing particles incorporated in a field-proven nitrile-based polymer. These particles swell via absorbing water, which in turn expands the rubber without being physically absorbed into the rubber matrix, which can adversely affect properties. An oil reactive section may utilize oleophilic polymers that absorb hydrocarbons into the matrix. This process may be a physical uptake of the hydrocarbon which swells, lubricates and decreases the mechanical strength of the polymer chain as it expands.
It would be desirable if the elastomers used in reactive element packers could be improved to swell to a greater volume than previously known. Such greater volumes would give greater tightness and continuity when the isolation tools engage the casing or the borehole wall.